from multiprocessing import Pool
import os, time, random 

def long_time_task(name):
    print('Run task %s (%s)' %(name, os.getpid()))
    start = time.time()
    time.sleep(random.random()*3)
    end=time.time()
    print('Task %s runs %0.2f seconds' % (name,(end- start)))
    
if __name__ == '__main__':
    print('Parent process %s.'%os.getpid())
    p = Pool(4)
    for i in range(5):
        p.apply_async(long_time_task,args=(i,))
    print('Waiting for all subprocessing done...')
    p.close()
    p.join()
    print('All subprocess done.')
    